The invention relates to a packer.
As shown in FIG. 1, for purposes of measuring characteristics (e.g., formation pressure) of a subterranean formation 31, a tubular test string 10 may be inserted into a wellbore that extends into the formation 31. In order to test a particular region, or zone 33, of the formation 31, the test string 10 may include a perforating gun 30 that is used to penetrate a well casing 12 and form fractures 29 in the formation 31. To seal off the zone 33 from the surface of the well, the test string 10 may be attached to, for example, a retrievable weight set packer 27 that has an annular elastomer ring 26 to form a seal (when compressed) between the exterior of the test string 10 and the internal surface of the well casing 12, i.e., the packer 27 seals off an annular region called an annulus 16 of the well. Above the packer 27, a recorder 11 of the test string 10 may take measurements of the test zone pressure.
The test string 10 typically includes valves to control the flow of fluid into and out of a central passageway of the test string 10. For example, an in-line ball valve 22 may control the flow of well fluid from the test zone 33 up through the central passageway of the test string 10. As another example, above the packer 27, a circulation valve 20 may control fluid communication between the annulus 16 and the central passageway of the test string 10.
The ball valve 22 and the circulation valve 20 may be controlled by commands (e.g., xe2x80x9copen valvexe2x80x9d or xe2x80x9cclose valvexe2x80x9d) that are sent downhole from the surface of the well. As an example, each command may be encoded into a predetermined signature of pressure pulses 34 see (FIG. 2) that are transmitted downhole via hydrostatic fluid that is present in the annulus 16. A sensor 25 may receive the pressure pulses 34 so that the command may be extracted by electronics of the string 10. Afterwards, electronics and hydraulics of the test string 10 operate the valves 20 and 22 to execute the command.
Two general types of packers typically may be used: the retrievable weight set packer 27 that is depicted in FIG. 1 and a permanent hydraulically set packer 60 that is depicted in FIG. 3. To set the weight set packer 27 (i.e., to compress the elastomer ring 26 to force the ring 26 radially outward), an upward force and/or a rotational force may be applied to the string 10 to actuate a mechanism (of the string 10) to release the weight of the string 10 upon the ring 26. However, rotational and translational manipulations of the test string 10 to set the packer 27 may present difficulties for a highly deviated wellbore and for a subsea well in which a vessel is drifting up and down, a movement that introduces additional motion to the test string 10. Additional drill collars 44 (one drill collar 44 being shown in FIG. 1) may be required to compress the ring 26. Slip joints 46 may be needed to compensate for expansion and contraction of the string 10.
Referring to FIG. 3, the hydraulically set packer 60 may be set by a setting tool that is run downhole on a wireline, or alternatively, the hydraulically set packer 60 may be run downhole on a tubing and set by establishing a predetermined pressure differential between the central passageway of the tubing and the annulus 16. Among the differences from the weight set packer 27, the packer 60 typically remains permanently in the wellbore after being set, a factor that may affect the number of features that are included with the packer 60. Furthermore, a separate downhole trip typically is required to set the packer 60. For example, a special tool maybe run downhole with the packer 60 to set the packer 60 in one downhole trip, and afterwards, another downhole trip may be required to run the test string 10. Because the test string 10 must pass through the inner diameter of a seal bore 62 of the packer 60, the outer diameter of the perforating gun 54 maybe limited, and stinger seals 52 of the test string 10 maybe damaged.
Thus, there exists a continuing need for a packer that addresses one or more of the above-stated problems.
In one embodiment of the invention, a packer for use inside a casing of a subterranean well includes a resilient element, a housing and a rupture disk. The resilient element is adapted to seal off an annulus of the well when compressed, and the housing is adapted to compress the resilient element in response to a pressure exerted by fluid of the annulus on a piston head of the housing. The housing includes a port for establishing fluid communication with the annulus. The rupture disk is adapted to prevent the fluid in the annulus from entering the port and contacting the piston head until the pressure exerted by the fluid exceeds a predefined threshold and ruptures the rupture disk.
In another embodiment, a method for setting a packer in a subterranean well includes isolating a resilient element from pressure being exerted from a fluid in an annulus of the well until the resilient element is at a predefined depth in the well. When the resilient element is at the predefined depth, the fluid in the annulus is allowed to compress the resilient element to seal off the annulus.
Advantages and other features of the invention will become apparent from the following description and from the claims.